1 /* SPDX-License-Identifier: GPL-2.0 */
3 * Copyright (C) 2014, 2015 Intel Corporation; author Matt Fleming
5 * Early support for invoking 32-bit EFI services from a 64-bit kernel.
7 * Because this thunking occurs before ExitBootServices() we have to
8 * restore the firmware's 32-bit GDT before we make EFI serivce calls,
9 * since the firmware's 32-bit IDT is still currently installed and it
10 * needs to be able to service interrupts.
12 * On the plus side, we don't have to worry about mangling 64-bit
13 * addresses into 32-bits because we're executing with an identity
14 * mapped pagetable and haven't transitioned to 64-bit virtual addresses
18 #include <linux/linkage.h>
20 #include <asm/page_types.h>
21 #include <asm/processor-flags.h>
22 #include <asm/segment.h>
26 SYM_FUNC_START(efi64_thunk)
33 leaq efi_gdt64(%rip), %rax
35 movl %eax, 2(%rax) /* Fixup the gdt base address */
45 * Convert x86-64 ABI params to i386 ABI
59 * Switch to gdt with 32-bit segments. This is the firmware GDT
60 * that was installed when the kernel started executing. This
61 * pointer was saved at the EFI stub entry point in head_64.S.
63 leaq efi32_boot_gdt(%rip), %rax
67 leaq efi_enter32(%rip), %rax
84 * Convert 32-bit status code into 64-bit.
89 andl $0x0fffffff, %ecx
90 andl $0xf0000000, %eax
98 SYM_FUNC_END(efi64_thunk)
102 * EFI service pointer must be in %edi.
104 * The stack should represent the 32-bit calling convention.
106 SYM_FUNC_START_LOCAL(efi_enter32)
107 movl $__KERNEL_DS, %eax
112 /* Reload pgtables */
118 btrl $X86_CR0_PG_BIT, %eax
121 /* Disable long mode via EFER */
124 btrl $_EFER_LME, %eax
129 /* We must preserve return value */
133 * Some firmware will return with interrupts enabled. Be sure to
134 * disable them before we switch GDTs.
143 btsl $(X86_CR4_PAE_BIT), %eax
151 btsl $_EFER_LME, %eax
163 btsl $X86_CR0_PG_BIT, %eax
166 SYM_FUNC_END(efi_enter32)
170 SYM_DATA_START(efi32_boot_gdt)
173 SYM_DATA_END(efi32_boot_gdt)
175 SYM_DATA_START_LOCAL(save_gdt)
178 SYM_DATA_END(save_gdt)
180 SYM_DATA_START(efi_gdt64)
181 .word efi_gdt64_end - efi_gdt64
182 .long 0 /* Filled out by user */
184 .quad 0x0000000000000000 /* NULL descriptor */
185 .quad 0x00af9a000000ffff /* __KERNEL_CS */
186 .quad 0x00cf92000000ffff /* __KERNEL_DS */
187 .quad 0x0080890000000000 /* TS descriptor */
188 .quad 0x0000000000000000 /* TS continued */
189 SYM_DATA_END_LABEL(efi_gdt64, SYM_L_LOCAL, efi_gdt64_end)